Blower motor for hvac systems

ABSTRACT

A blower motor assembly having a variable speed motor that is suitable for direct, drop-in replacement in a residential HVAC (heating, ventilation, and air conditioning) system that employs a PSC motor. The blower motor assembly includes at least a neutral input and two hot AC line connections, one for connection to the heating power source and the other to the cooling power source. A sensing circuit senses which of the inputs is energized by sensing either voltage or current on the inputs. The sensing circuit delivers a corresponding signal to a motor controller to control the speed of the variable speed motor. The blower motor assembly may also be equipped with additional hot AC inputs, more than one neutral line, and several sensing circuits for sensing current or voltage in the hot inputs and/or the neutral lines for controlling various aspects of the variable speed motor.

RELATED APPLICATIONS

The present application is related to co-pending U.S. application Ser.No. ______, filed Sep. 8, 2008, entitled “BLOWER MOTOR FOR HVACSYSTEMS”; U.S. application Ser. No. ______, filed Sep. 8, 2008, entitled“BLOWER MOTOR FOR HVAC SYSTEMS”; U.S. application Ser. No. ______, filedSep. 8, 2008, entitled “BLOWER MOTOR FOR HVAC SYSTEMS”; U.S. applicationSer. No. ______, filed Sep. 8, 2008, entitled “BLOWER MOTOR FOR HVACSYSTEMS”; and U.S. application Ser. No. ______, filed Sep. 8, 2008,entitled “BLOWER MOTOR FOR HVAC SYSTEMS”, all of which are incorporatedherein in their entirety by reference.

FIELD OF INVENTION

The present invention relates to blower motors and controls used inresidential heating, ventilation, and air conditioning (HVAC) systems.More particularly, embodiments of the invention relate to a replacementblower motor assembly that can be connected to the standard powerterminals used for a permanent split capacitor (PSC) motor and such ablower motor assembly that can be used in Original EquipmentManufacturer (OEM) applications and other applications.

BACKGROUND

HVAC system efficiency increases have provided considerable reductionsin energy use. For example, many high efficiency furnaces, airconditioners, and air handlers now have efficiencies (AFUE ratings)greater than 90%. However, the blower motors used to move the air inthese systems have not seen significant efficiency improvements and havemuch lower efficiencies. As furnaces and air conditioners have becomemore efficient, the fraction of total energy consumption for HVACsystems attributed to the blower motors has increased, thus makingblower motors a greater contributor to the overall system energy use.

Blower motor inefficiencies are magnified when a blower motor isoperated for extended hours beyond that needed solely for heating andcooling. For example, some users frequently choose to let their HVACsystem's blower motor operate continuously by setting a fan controlswitch to the “on” position. This circulation mode of operation reducestemperature stratification, minimizes start drafts from duct work,improves humidity control, and increases the effectiveness of associatedair cleaners employed in conjunction with the HVAC system. By selectingthe “on” position, the blower motor operates continuously, and theassociated thermal feature, (i.e., either heating or cooling) operateson the “demand” setting of the thermostat. When in the “on” position,the blower motor typically operates at the speed used for cooling, evenwhen the thermostat is set to heat mode. This speed is usually well inexcess of what is necessary to achieve the air circulation benefitsoutlined above. This causes excess energy usage and noise. In addition,with the blower switch in the “on” position, the unit no longer is ableto select the system speed for cooling or heating and insteadcontinuously runs at the continuous fan speed. Even when systems aredesigned to select the proper speed in a multiple speed motor, forexample, as disclosed in U.S. Pat. No. 4,815,524, the speed availablefor blower “on” use is higher than necessary for such operations, andcan be responsible for cold spot corrosion, requiring a shut down perioddisclosed in the '524 patent. The increased operation time thereforeleads to greater energy use.

Many of the above-described inefficiencies result from the type ofblower motor used in HVAC systems. HVAC systems traditionally use fixedspeed or multiple speed permanent split capacitor (PSC) motors. Thesemotors generally have two independent power connections to accommodateheating or cooling modes of operation. The heating or cooling powerinputs are normally connected to different winding taps in the PSC motorto provide somewhat different operating speeds for the blower in therespective modes of operation. More than two taps can be designed intothe PSC motor, allowing the OEM or installer to select the operatingspeed by appropriate connection of the taps to the respective heatingand cooling power connections. The energizing of these AC powerconnections to the motor is controlled by activation of a temperatureswitch and a relay driven from the thermostat.

An example of a fixed speed PSC motor M1 used in residential HVACsystems is shown in FIG. 1. In this configuration, the single phase ACsupply voltage (normally 115 VAC or 230 VAC) is supplied by connectionsL1 and N, where L1 represents the hot side of the AC supply, and N isneutral, which is at earth potential in a typical 115 VAC residentialdistribution system. (In normal 230 VAC systems, another hot supply linewould be substituted for the neutral line N.) The power to the motor iscontrolled by a relay R1 and a switch S1, which are both shown in theirnon-energized positions. The blower relay R1 is controlled by athermostat.

In the position shown in FIG. 1, which is the normal position for theheating mode of operation, AC voltage is supplied to a power inputconnection L1H motor connection any time fan control switch S1 closes.The fan control switch S1 closes whenever the air temperature in theheat exchanger exceeds a predetermined setpoint. For a gas furnacesystem, this happens a short time after the gas burner is activated bysignals from the thermostat once the thermostat reaches a triggertemperature. When fan control switch S1 closes, AC power is supplied tothe motor M1, which will then start and run. The speed of motor M1 is afunction of motor design, tap selection in the motor, blowercharacteristics and the aerodynamic system impedance. Motor M1 stopswhen fan control switch S1 turns off, which happens whenever the heatexchanger air temperature decreases below the setpoint.

Similarly, when the thermostat demands blower operation because ofcooling demand, blower relay R1 closes and energizes the L1C motorconnection, thus operating the motor at its cooling mode speed. Bloweroperation ceases when signals from the thermostat de-energize blowerrelay R1.

Referring now to FIG. 1A, another fixed speed PSC motor used inresidential HVAC systems is shown. The motor has four winding taps toaccommodate two heating fan speeds and two cooling speeds. The fan speedis controlled by a furnace control board with a cool/heat relay, alow/high cool relay, and a low/high heat relay. Other HVAC systems mayinclude two heating stages and a single cooling stage or any othercombination of heating and cooling speeds.

PSC motors are reasonably efficient when operated at high speed, buttheir efficiencies may drop down into the 20% range when operated at lowspeeds. Because air conditioner evaporator coils need higher airflowthan furnace heat exchangers, the blower motor operates at a lower speedduring furnace operation, where it is less efficient, and at an evenlower speed still during continuous fan “on” operation, where it isleast efficient.

Because of the above-described inefficiencies of PSC motors, many newerHVAC systems use variable speed motors such as brushless permanentmagnet (BPM) motors and corresponding electronic variable speed motorcontrollers. The speed of a BPM can be electronically controlled and setspecifically to match the airflow requirements for each application,thus permitting more efficient operation. Also, BPM motors use powerapproximately proportional to the cube of motor speed, whereas PSCmotors use power approximately proportional to motor speed therefore, asmotor speed drops, BPM motors use less power than PSC motors over a widerange of motor speeds. This is particularly important when operating theblower continuously for circulation as described above.

While variable speed motors are often superior to PSC motors, replacingan existing PSC motor with a variable speed motor in a system similar tothat illustrated in FIG. 1A has required costly, time-consuming, andcomplex changes in the mechanical, wiring, or control configuration ofthe system. Variable speed motor systems configured for replacement ofPSC motors in existing HVAC systems have been developed, but they haverelatively complicated control and sensing systems. For example, somesystems require the installation of a temperature sensor in the outletductwork of the HVAC system for controlling the speed of the motor basedupon temperature. In other replacement systems, the installation of areplacement motor requires continuous power connection to the motor andthe connection of low voltage control signals directly from thethermostat to the motor. Making these connections can be cumbersome anddifficult in an existing HVAC system. Moreover, these known systems lackthe sensitivity to operate blowers at low operating speeds.

Another limitation of existing PSC and BPM motors is that HVAC OEMsoften require motors with unique operating parameters (torque load, fanspeed, rotation direction, etc.) to optimize the performance of theirHVAC components. While multiple speed PSC motors and BPM motors offersome operational options, many of their operating parameters are fixedafter manufacture and cannot be easily changed. Motor manufacturers,installers, and service contractors therefore must stock a diverseinventory of blower motors to accommodate the various different modelsof HVAC equipment.

It would therefore be desirable to provide an improved “drop-in”replacement for a PSC motor in an HVAC system to realize the advantagesof a variable speed blower motor without requiring significant changesto the HVAC system. It would be further advantageous to reduce thecomplexity of such replacement systems by utilizing simple controlcircuits and eliminating the need for additional wiring, such as thatused in conjunction with traditional variable speed motors and existingreplacement variable speed motor systems. It would also be advantageousto provide an HVAC blower motor that could be customized to accommodatemore HVAC systems.

SUMMARY

The present invention solves many of the above-described problems andother problems and provides a distinct advance in the art of HVAC blowermotors and other electric motors.

One embodiment of the invention is a blower motor assembly broadlycomprising a rectifier, a novel sensing circuit, a variable speed motor,and the motor's associated motor controller and power converter. Powerto the blower motor assembly is provided via the same set of power inputconnections provided to the PSC motor M1 of FIG. 1, i.e., L1C, L1H andneutral N, so that the blower motor assembly can serve as a drop-inreplacement for that portion of the PSC motor of FIG. 1 enclosed by therectangle 10A.

One embodiment of the sensing circuit includes a current transformer CT,a resistor R1, a resistor R2, a diode D1, a transistor Q1, a resistorR3, a capacitor C1, and a resistor R4. Two primary benefits of thesensing circuit are its simplicity and sensitivity. Because the circuitcomprises only a small current transformer, 4 resistors, a capacitor, asingle transistor, and a diode, it is relatively simple to construct andfits in a small area such as on a small power input connector. Moreover,the use of a single transistor provides a relatively passive design thateffectively senses current in L1C or L1H with a small currenttransformer. This is important, because a more sensitive sensing circuitcan be used to sense a continuous fan speed input connection or otherinput carrying less current as described in more detail below.

Another embodiment of the invention is a blower motor assemblyconfigured to replace a PSC motor with more than two hot powerconnections such as a PSC motor with a high speed, a medium speed, a lowspeed, and a continuous fan speed. The blower motor assembly of thisembodiment may include five or more power inputs, three sensor circuitsfor detecting current in the five inputs, and combinational logic forcontrolling operation of the blower motor as a function of the currentsensed by the three sensor circuits.

Another embodiment of the invention is a blower motor assembly equippedwith a pair of neutral line inputs, for example a CW neutral input and aCCW neutral input. Power may be connected to either of the two neutralinputs to select a blower fan rotation or any other parameter of themotor. A sensing circuit is configured for sensing current in one of theneutral inputs and for providing a corresponding signal to the motorcontroller for controlling an operational parameter of the motor such asthe motor's rotation direction.

Another embodiment of the invention aims to reduce the amount of highcurrent wires brought into the enclosure of the blower motor assembly.Known HVAC blower motors are enclosed within a two-piece can, with themotor itself positioned in one of the portions and the motor controllerand other electronics positioned in the other. Those skilled in the artwill appreciate that known variable speed motor enclosures can include amyriad of wiring and electronics that are often difficult to identifywhen maintenance is required. Moreover, an abundance of wiring in amotor enclosure can cause magnetic interference between the wires andthe motor itself. The present invention provides a novel power inputconnector that supports the input power connections and the sensingcircuits described above near the exterior of the motor can to reducethe number of high current wires extending into the can.

Another embodiment of the invention is a method for automaticallysensing proper rotation direction of an HVAC blower motor. The designand orientation of the ducts, heat exchanger, evaporator coils, andother components of an HVAC system often necessitate either a CW or aCCW blower fan. HVAC installers therefore must stock both CW and CCW PSCmotors for replacement purposes. Reversible motors can replace either aCW or a CCW PSC motor, but the installer still must be careful to selectthe proper rotation direction or else the HVAC system will not operateproperly. The rotation sensing method of the present invention solvesthese problems by sensing the motor direction and automaticallycorrecting it if it is wrong.

Another embodiment of the invention provides methods to adjust thetorque settings of an HVAC blower motor. HVAC OEMs often desire blowermotors specifically designed to work with their HVAC equipment. With PSCmotors, motor manufacturers can accommodate such requests by changingthe motor winding taps on their motors to achieve the desired torqueratings. Unfortunately, changing the motor winding taps to accommodateevery OEM's exact specifications is time-consuming and costly andrequires that many slightly modified motors be manufactured and stocked.The present invention makes it easier to customize HVAC motors forparticular OEMs' needs, by providing a simple method of adjusting thetorque values of a blower motor without changing the motor's windingtaps or otherwise altering the motor's physical design. In particular,the torque values of the motor may be modified during manufacturingwithout the use of a computer or other device capable of individuallychanging all of the torque memory values stored in the motor memory.Instead, the torque values are automatically modified in the motor basedupon a single maximum torque desired in the motor, as described herein.

By constructing a blower motor assembly as described herein, numerousadvantages are realized. For example, the blower motor assembly of thepresent invention can be used as a relatively low-cost replacement foran inefficient fixed speed motor in an existing HVAC system. Thereplacement blower motor assembly uses less energy, allows foreconomical continuous fan operation, and is quieter than conventionalfixed speed motors. Moreover, the blower motor assembly can be quicklyand easily installed without requiring changes to the mechanicalconfigurations, wiring, or control of the HVAC system. Embodiments ofthe blower motor assembly and related methods also permit a standardsized motor to be customized for many different applications, thusreducing the number of differently configured motors that must bemanufactured and stocked. Still further, the sensing circuit of theblower motor assembly is simpler, more sensitive, and more compact thanthe sensing circuitry in prior art replacement blower motor assemblies.The blower motor assembly of the present invention may also be used inOEM and other non-replacement applications. Moreover, many aspects ofthe present invention may be separately useful without the motor, bothfor OEM and/or replacement use.

These and other important aspects of the present invention are describedmore fully in the detailed description below.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

An exemplary embodiment of the present invention is described in detailbelow with reference to the attached drawing figures, wherein:

FIG. 1 is a schematic circuit diagram of a prior art blower motor andassociated control circuitry for an HVAC system.

FIG. 1A is a schematic circuit diagram of a prior art blower motor andassociated control circuitry for another HVAC system.

FIG. 2 is a schematic circuit diagram of a blower motor assemblyconstructed in accordance with an embodiment of the invention and shownwired to associated control circuitry of an HVAC system.

FIG. 3 is a schematic circuit diagram of an exemplary rectifier of theblower motor assembly shown in FIG. 2.

FIG. 4 is a schematic circuit diagram of another exemplary rectifier ofthe blower motor assembly shown in FIG. 2.

FIG. 5 is a schematic circuit diagram showing details of an embodimentof the sensing circuit of the blower motor assembly of FIG. 2.

FIG. 6 is a schematic circuit diagram of a blower motor assemblyconstructed in accordance with another embodiment of the invention andhaving three sensing circuits.

FIG. 7 is a truth table representing a logic function of the motorcontroller of the blower motor assembly.

FIG. 8 is a schematic circuit diagram of portions of a blower motorassembly constructed in accordance with another embodiment of theinvention and having a sensing circuit for sensing power in a neutralline.

FIG. 9 is a perspective view of a power input connector constructed inaccordance with another embodiment of the invention.

FIG. 10 is an exploded view of components of a power input connectorconstructed in accordance with another embodiment of the invention.

FIG. 11 is a perspective view of the power input connector of FIG. 10shown assembled and mounted in a motor enclosure.

FIG. 12 is a flow diagram depicting a method for determining the properrotation direction of a blower motor.

FIG. 13 is a flow diagram depicting another method for determining theproper rotation direction of a blower motor.

FIG. 14 is a schematic diagram of a torque adjustment mechanismconstructed in accordance with an embodiment of the invention and showncoupled with a blower motor.

FIG. 15 is a schematic circuit diagram showing details of the torqueadjustment mechanism.

The drawing figures do not limit the present invention to the specificembodiments disclosed and described herein. The drawings are notnecessarily to scale, emphasis instead being placed upon clearlyillustrating the principles of the invention.

DETAILED DESCRIPTION

The following detailed description of the invention references theaccompanying drawings that illustrate specific embodiments in which theinvention can be practiced. The embodiments are intended to describeaspects of the invention in sufficient detail to enable those skilled inthe art to practice the invention. Other embodiments can be utilized andchanges can be made without departing from the scope of the invention.The following detailed description is, therefore, not to be taken in alimiting sense. The scope of the invention is defined only by theappended claims, along with the full scope of equivalents to which suchclaims are entitled.

Referring now to FIG. 2, a blower motor assembly 10 constructed inaccordance with an embodiment of the invention is shown. The illustratedblower motor assembly 10 broadly comprises a rectifier 12, a novelsensing circuit 14, a variable speed motor 16, and the motor'sassociated motor controller and power converter 18. Power to the blowermotor assembly 10 is provided via the same set of power inputconnections provided to the PSC motors M1 of FIGS. 1 and 1A, i.e., L1C,L1H, and neutral N, so that the assembly 10 can serve as a drop-inreplacement for that portion of the PSC motors of FIGS. 1 and 1Aenclosed by the rectangles 10A and 10B. However, the blower motorassembly 10 and other embodiments of the invention may also be used inOEM and other non-replacement applications. Moreover, many aspects ofthe present invention may be separately useful without the motor, bothfor OEM and/or replacement use.

Returning to FIG. 2, the rectifier 12 is conventional and converts theAC power on the power input connections L1C, L1H and neutral N to DCpower and delivers the DC power to the motor controller 18. FIGS. 3 and4 show two versions of the rectifier, generally indicated 12 a and 12 b,with the rectifier 12 a being used when the sensing circuit 14 isconfigured for voltage sensing and the rectifier 12 b being used whenthe sensing circuit is configured for current sensing. As shown in FIGS.3 and 4, both versions of the rectifier 12 a and 12 b include at least arectifier bridge comprising diodes D1, D2, D3, and D4. For voltagesensing, the rectifier 12 a must be modified to decouple the powersources, since if they are not decoupled, the L1C and L1H connectionswould have a tie point, making it impossible to determine the source ofthe voltage. FIG. 3 shows one way to decouple the AC supply inputs. Anadditional leg comprising diodes D5, D6 is added to the rectifier 12 ato decouple power sources L1C and L1H, thus allowing the sensing circuit14 to determine the source of the input power.

With current sensing shown in FIG. 4, the L1C and L1H inputs areconnected together at an input 20 of the rectifier bridge. A currentsense point 22 is ahead of the input 20. It will be recognized that,although sense point 22 is shown here in the L1C input, with appropriatemodifications, it could alternately be in the L1H input. The currentsensing technique requires no additional bridge diode leg, as does thevoltage sensing technique, but does require isolation between the sensepoint 22 and a common DCN.

The sensing circuit 14 monitors L1C or L1H inputs and generates acorresponding logic level signal CR1 whenever AC power is detected inone of the inputs. Voltage sensing or current sensing may be used asmentioned above. Since the sensing scheme is used only to detect thepresence or absence of voltage or current on the sensed input,significant accuracy is not required, so the complexity of either typeof sense circuitry can be reduced.

Because a blower system characteristically has an output powerproportional to the cube of the speed of the motor driving the fan, andsince the current sensing technique is sensitive to the power fed to themotor, the current detection level and hysteresis must be selected toensure that the correct sensing of the AC source is achieved over theoperating speed and torque range of the motor. It will also beunderstood that current sensing can be done by a number of well-knownsensing techniques, including but not limited to, for example, shuntsensors or current transformers.

FIG. 5 illustrates a current sensing embodiment of the sensing circuit14 in more detail. The sensing circuit 14 includes a current transformerCT, a resistor R1, a resistor R2, a diode D1, a transistor Q1, aresistor R3, a capacitor C1, and a resistor R4. In an exemplaryembodiment, the current transformer CT is a toroidal core transformerhaving about 30 or more turns, R1 is approximately 510 ohms, R2 isapproximately 1K ohms, D1 is a 1N4148 high speed switching diode, Q1 isa 2N3904 NPN-type amplifying transistor, R3 is approximately 10 ohms, C1is 0.1 μF, and R4 is approximately 100K ohms. But the particular sizes,properties, and types of these components are only provided to describea particular exemplary embodiment of the invention and can be changedwithout departing from the scope of the claims.

The current transformer CT is inductively coupled with the L1C input ofthe AC power input connections and senses when current is flowing in thecooling power input connection L1C. The current transformer CT couldinstead be coupled with the heating power input connection L1H. CTcouples the sensed current to the base of transistor Q1. R1 serves as aload resistor for defining a minimum load on the current transformer CTand R2 limits the peak current delivered to Q1. D1 protects the baseemitter junction of Q1.

Q1 amplifies the pulses sensed by CT and delivers the amplified pulsesthrough its collector to C1. R3 limits the current to C1 toapproximately 300 milliamps. R4 serves as a pull-up resistor and chargesC1 up to the illustrated 5 volt supply. The pulses from the transistorQ1 cause C1 to repetitively discharge, causing the input to the motorcontroller 18 to change, thus indicating current through L1C. The motorcontroller 18 may include a microprocessor and/or other electronics forsensing the signals from the sensing circuit 14. When currenttransformer CT has saturated or the current through L1C ends, R4 chargesC1 back up to the 5 volt supply value. The goal is for the voltage of C1to be below the logic threshold of the processor in the motor controller18 for 3 to 5 milliseconds for accurate sensing.

When the sensing circuit 14 senses current in L1C as described above,the motor controller 18 operates the motor 16 to drive the blower fan ata speed selected for the cooling mode of the corresponding HVAC system.If the sensing circuit senses no current in L1C and when the switch S1and relay R1 of FIG. 1 are both closed, the motor controller 18 operatesthe motor 16 to drive the blower at a speed selected for the heatingmode of the corresponding HVAC system. The fan speeds for the cooling,heating, and other modes of operation may be programmed into the motorcontroller 18 during manufacture or may be selected by other means. Thesignals generated by the sensing circuit 14 and fed to the motorcontroller 18 can be used to select the speed of the motor, but may alsobe used to control any other parameter, such as, but not limited to, fandirection or torque.

Two primary benefits of the sensing circuit 14 of the present inventionare its simplicity and sensitivity. Because the sensing circuit 14comprises only a small current transformer, four resistors, a capacitor,a single transistor, and a diode, it is relatively simple to constructand fits in a small volume, such as on a small power input connector, anexample of which is described in more detail below. Moreover, the use ofa single transistor provides a relatively passive design thateffectively senses current in power inputs L1C or L1H with a smallcurrent transformer. Known prior art sensing circuits for replacementHVAC blower motors use Schmitt trigger logic buffers to define a voltagelevel to switch between heating and cooling modes of operation. Therequired voltage level for these prior art sensing circuits is higherthan that needed for a single transistor, thus necessitating a largercurrent transformer to achieve the same sensing sensitivity. This isimportant, because a more sensitive sensing circuit, such as the sensingcircuit 14 disclosed herein, that can sense an instantaneous peakcurrent as low as about two amps in a power input, can be used to sensea continuous fan speed input connection or other input carrying lesscurrent, as described in more detail below. In another exemplaryembodiment, the sensing circuit 14 can sense an instantaneous peakcurrent as low as about one amp in a power input.

The discussion up to this point has been for a blower motor assemblyconfigured to replace a PSC motor M1 with two hot power connections, L1Cand L1H. However, some PSC motors have additional winding taps toprovide additional operating speeds, such as a high speed, a mediumspeed, a low speed, and a continuous fan speed. Blower motor assembliesconfigured for replacing these types of PSC motors must have additionalpower input connections and sensing circuits for sensing current in thepower inputs. FIG. 6 illustrates a blower motor assembly 100 configuredto replace such a PSC motor. The blower motor assembly 100 of FIG. 6 mayalso be used to replace a two-speed PSC motor, with the extra powerinput connections and sensing circuits providing an installer severaldifferent fan speeds to replace the two speeds of the PSC motor.

As illustrated, the exemplary blower motor assembly 100 includes sixpower connections IN1-IN6 and three sensing circuits, generallyindicated 140 a, 140 b, and 140 c, for sensing current in the inputsIN1-IN6 and for providing associated signaling to the motor controller18 for selecting a corresponding fan speed or other motor parameter.

The power inputs IN1-IN6 may correspond to any set of operatingparameters for the motor. In one exemplary embodiment, IN1 maycorrespond to a highest blower speed (e.g. 100%), IN2 may correspond toa medium/high blower speed (e.g. 90%), IN3 may correspond to a mediumblower speed (e.g. 80%), IN4 may correspond to a medium/low blower speed(e.g. 70%), IN5 may correspond to a low blower speed (e.g. 60%), and IN6may correspond to a minimum continuous fan blower speed (e.g. 50%).

The three sensing circuits 140 a-c are substantially identical and areeach configured for sensing the presence of current in one or more ofthe power inputs IN1-IN6. Specifically, sensing circuit 140 a sensescurrent in power inputs IN1 and IN2, sensing circuit 140 b sensescurrent in IN3 and IN4, and sensing circuit 140 c senses current in IN5.IN6 is not sensed by any of the sensing circuits as explained below.

Each of the sensing circuits 140 a-c operates in the same manner as thesensing circuit 14 of FIG. 5 and comprises a current transformer CT, aresistor R1, a resistor R2, a diode D1, a transistor Q1, a resistor R3,a capacitor C1, and a resistor R4. In an exemplary embodiment, each CTis a toroidal core transformer having about 30 or more turns, each R1 isapproximately 510 ohms, each R2 is approximately 1K ohms, each D1 is a1N4148 high speed switching diode, each Q1 is a 2N3904 NPN-typeamplifying transistor, each R3 is approximately 10 ohms, each C1 isapproximately 0.1 μF, and each R4 is approximately 100K ohms. Again, theparticular sizes, properties, and types of these components are providedto describe a particular exemplary embodiment of the invention and canbe changed without departing from the scope of the claims.

In accordance with an important aspect of the invention, the motorcontroller 18 receives signals from each of the sensing circuits 140 a-cand selects a motor speed or other motor parameter based on acombination of the signals. FIG. 7 shows an exemplary truth table thatmay be utilized by the motor controller 18 to select a motor operatingspeed or other motor parameter based on the sensing of current inIN1-IN6. The first line of the truth table shows that sensing circuit140 a sensed current but sensing circuits 140 b and 140 c did not (“X”denotes sensing of current). This indicates that only power input IN1was energized because if any of IN2-IN5 (IN6 will be discussed later)were also energized, sensing circuits 140 b or 140 c also would havesensed current. The motor controller 18 therefore selects a motor speedor other motor parameter (e.g., torque, power, airflow) associated withinput IN1. For example, if input IN1 corresponds to the highest speedtap of the replaced PSC motor M1, the motor controller 18 may operatethe variable speed motor 16 at a maximum speed (or highest selectedspeed).

The second line of the truth table shows that sensing circuits 140 a and140 b both sensed current but sensing circuit 140 c did not. Thisindicates that power input IN2 was energized because it is the onlypower input sensed by both sensing circuits 140 a and 140 b. The motorcontroller 18 therefore selects a motor speed or other parameterassociated with IN2. The third line of the truth table shows that onlysensing circuit 140 b sensed current, thus indicating that power inputIN3 was energized because only IN3 is monitored by sensing circuit 140 balone. The motor controller 18 therefore selects a motor speed or othermotor parameter associated with IN3. The fourth line of the truth tableshows that sensing circuits 140 b and 140 c sensed current, thusindicating that power input IN4 was energized because only it is sensedby both these sensing circuits. The motor controller 18 thereforeselects a motor speed or other motor parameter associated with IN4. Thefifth line of the truth table shows that only sensing circuit 140 csensed current, thus indicating that power input IN5 was energized,because IN5 is the only power input sensed by this sensing circuit. Themotor controller 18 therefore selects a motor speed or other motorparameter associated with IN5.

The sixth line of the truth table indicates an additional operating modeenabled by the blower motor assembly 100 of FIG. 6. The sixth line showsthat none of the sensing circuits 140 a, 140 b, 140 c sensed current,indicating that none of the power inputs IN1-IN5 were energized. Thesixth power input, IN6, is not sensed by the sensing circuits 140 a, 140b, 140 c and may be associated with a continuous fan speed for the motor16. With this sixth input IN6, the motor controller 18 could operate theblower motor 16 at its lowest speed at all times until the HVAC systemcalls for heating or cooling and an associated higher blower speed.

The above-described blower motor assembly 100 permits selection betweenfive or six motor speeds (or selection of five or six other motorparameters) with only three sensing circuits 140 a-c. Moreover, each ofthe sensing circuits is simple to construct, relatively passive, andmore sensitive than prior art sensing assemblies as discussed above.

In another exemplary embodiment of the invention, the blower motorassembly 10 or 100 may be equipped with a pair of neutral line inputs,for example a CW neutral input and a CCW neutral input. Power may beconnected to either of the two neutral inputs to select a blower fanrotation direction or any other parameter of the motor.

FIG. 8 illustrates a sensing circuit 1400 configured for sensing currentin one of the neutral inputs and for providing a corresponding signal tothe motor controller 18. The neutral line sensing circuit 1400 is shownsensing the CW neutral line but instead could sense the CCW neutralline. The sensing circuit 1400 operates in the same manner as thesensing circuit 14 of FIG. 5 described above and includes a currenttransformer CT, a resistor R1, a resistor R2, a diode D1, a transistorQ1, a resistor R3, a capacitor C1, and a resistor R4. In an exemplaryembodiment, CT is a toroidal core transformer having about 30 or moreturns, R1 is approximately 510 ohms, R2 is approximately 1K ohms, D1 isa 1N4148 high speed switching diode, Q1 is a 2N3904 NPN-type amplifyingtransistor, R3 is approximately 10 ohms, C1 is approximately 0.1 μF, andR4 is approximately 100K ohms. Again, the particular sizes, properties,and types of these components are provided to describe a particularexemplary embodiment of the invention and can be changed withoutdeparting from the scope of the claims.

As mentioned above, an installer can connect a neutral power cable toeither the CW neutral input or the CCW neutral input to select betweendifferent motor parameters. In one embodiment, the CW and CCW inputs areused to select the fan direction for a reversible blower motor 16.Specifically, if the sensing circuit 1400 senses current in the CWinput, the motor controller 18 operates the motor in a CW fan rotation,as directed by the installer. Conversely, if the sensing circuit 1400senses no current in the CW input, the motor controller 18 operates themotor in a CCW fan rotation, as directed by the installer.

In other embodiments, an installer can connect a neutral power cable tothe CW or CCW neutral inputs to select between other motor parameters,such as speed tables, torque tables, mode selection, blowercoefficients, and rotation direction of the motor. In one example, theCW input may be associated with a first speed table and the CCW inputmay be associated with a second speed table. In this case, the CW andCCW inputs may instead be labeled as “Speed Table 1” and “Speed Table 2”inputs). Here are two exemplary first and second speed tables that maybe stored in memory of the motor controller:

Speed Table 1  IN1 - 100% IN2 - 90% IN3 - 80% IN4 - 70% IN5 - 60%

Speed Table 2 IN1 - 95% IN2 - 85% IN3 - 75% IN4 - 65% IN5 - 55%

When the sensing circuit 1400 of FIG. 8 senses current in the CW neutralinput (or Speed Table 1 input), it signals the motor controller 18 touse the first speed table. The motor controller then uses thecorresponding speed values for the power inputs IN1-IN5 described above.For example, if the sensing circuit 1400 of FIG. 8 senses current in theCW or Speed Table 1 input, and the sensing circuits 140 a-c of FIG. 6and truth table of FIG. 7 determine that current is flowing in IN3, themotor controller operates the fan at a speed (or torque) of 80% fromSpeed Table 1. Similarly, if the sensing circuit of FIG. 8 senses nocurrent in the CW (or Speed Table 1) input, and the sensing circuits 140a-c of FIG. 6 and truth table of FIG. 7 determine that current isflowing in IN4, the motor controller operates the fan at a speed of 65%from Speed Table 2. The speed tables listed and described above can ofcourse be replaced with other speed tables. These different speed tablesprovide for system customization, such as between heating and coolingoperating modes, different types and sizes of mating equipment (e.g.,fans, air conditioners), and different environmental conditions (e.g.,different climatic regions).

For example, the two CW and CCW neutral inputs and corresponding neutralsensing circuit 1400 may also be used to select between fast and slowmotor speed ramps. A fast ramp-up could take 2-5 seconds similar to theway a PSC motor starts up. A slow ramp-up could take 30 seconds toslowly and quietly ramp up to the selected speed, so as to produce lessnoise and vibration and be generally less noticeable in a homeenvironment. The CW neutral input could be assigned to fast ramp-up andthe CCW neutral input could be assigned to the slow ramp-up. When theneutral sensing circuit 1400 senses current in the CW neutral input, itsignals the motor controller 18 to use the faster ramp-up. In most HVACoperating modes, the circulation airflow does not have to turn oninstantly because there is a time lag between when the thermostat callsfor heat and the heat exchanger is warmed up sufficiently to heat theair blown over the heat exchanger. There would also be a delay incooling mode for the evaporator coil to become cooled down sufficientlyto cool the air moving through the coil. Thus, the fast and slowramp-ups may include an initial delay, such as between about 30 secondsand about 60 seconds.

Another aspect of the invention aims to reduce the amount of highcurrent wires brought into an enclosure 26 (FIG. 11) of the blower motorassembly 10 or 100. Known HVAC blower motors M are enclosed within atwo-piece can, with the motor itself positioned in one of the portionsand the motor controller and other electronics positioned in the other.Those skilled in the art will appreciate that known variable speed motorenclosures include a myriad of wiring and electronics that are oftendifficult to identify when maintenance is required. Moreover, anabundance of wiring in a motor enclosure 26 can cause magneticinterference between the wires and the motor itself. To alleviate theseproblems, the present invention includes a novel power input connector24 (FIGS. 9-11) that supports the input power connections and thesensing circuits described above near the exterior of the motor can.

FIG. 10 illustrates an embodiment of the power input connector,generally indicated 24, shown partially disassembled and FIG. 11 showsthe assembled power connector mounted within an opening of the motorcontroller portion of the motor enclosure, or can, 26. The exemplarypower input connector 24 includes a pair of circuit boards 28, 30, topand bottom covers 32, 34, and a front face 36.

The power input connector 24 is assembled by stacking the circuit boards28, 30 and then sandwiching the circuit boards between the covers 32, 34and shielding one edge of each of the circuit boards with the face 36.The assembled power input connector 24 is then inserted in theillustrated opening 27 of the motor can 26. Note that the illustratedpower input connector is of one exemplary construction and may bereadily modified without departing from the scope of embodiments of theinvention, such as when modified for mass manufacture. For example, FIG.9 illustrates another embodiment of the power input connector, generallyindicated 24 a, that may be more suitable for mass production. Manyother variations of the power input connector also fall within the scopeof the present invention.

Returning to FIG. 10, the first circuit board 28 supports five hot ACline inputs 38, 40, 42, 44, 46 (e.g. IN1-IN5) and components of thesensing circuits 140 a, 140 b, and 140 c of FIG. 6, including the threecurrent transformers CT. Jumpers may be connected to the inputs 38-46and threaded through the middles of the current transformers CT so thecurrent transformers can sense current in the inputs as described above.Placement of the current transformers CT on the circuit board 28adjacent the AC line inputs 38-46 and the use of short, relatively smalljumpers reduces the amount of high current wiring that enters theenclosure 26.

The second circuit board 30 supports a pair of neutral inputs 48, 50(e.g. CW neutral and CCW neutral), a ground input 52, and components ofthe neutral line sensing circuit 1400 of FIG. 8, including its currenttransformer CT. A jumper may be connected to one of the neutral inputs48, 50 and threaded through the current transformer CT. As with thesensing circuits 140 a, 140 b, 140 c for the AC line inputs, placementof the neutral sensing current transformer CT on the circuit board 30adjacent the neutral line inputs 48, 50 reduces the amount of highcurrent wiring that enters the enclosure 26.

The second circuit board 30 may also support a novel in-rush protectioncircuit, generally indicated 54, comprising an in-rush limiting resistor56 and a relay 58. Prior art HVAC motors typically include an NTCthermistor or other type of in-rush limiting device. However, repeatedlyapplying power to the motor controller eventually damages the NTCin-rush limiter, bridge rectifier, and bus caps. The charging resistor56 limits the initial current flow to the DC bus and the relay 58bypasses the resistor 56 once the bus is charged. This reduces thein-rush currents and prolongs the life of the bridge rectifier, buscaps, and external relays and switches used to apply power to the motor.

Another embodiment of the invention is a method for automaticallydetecting proper rotation direction of an HVAC blower motor. The designand orientation of the ducts, heat exchanger, evaporator coils, andother components of an HVAC system often necessitate either a CW or aCCW blower fan. HVAC installers therefore must stock both CW and CCW PSCmotors for replacement purposes. The blower motor assemblies 10, 100 ofthe present invention may include reversible motors 16 for replacingeither a CW or a CCW PSC motor. But the installer must be careful toselect the proper rotation direction, or the HVAC system will notoperate properly. The rotation detecting method of the present inventionsolves these problems by detecting the response of the motorautomatically correcting an improper direction of rotation.

The rotation detecting method considers the fact that most HVAC motorsattached to a unidirectional fan exhibit noticeably differentcharacteristics when rotating the fan in the wrong direction, ascompared with rotating the fan in the intended direction. Consideringtorque as an exemplary characteristic, most HVAC motors have anoticeably lower torque when rotating the fan in the wrong direction, ascompared with rotating the fan in the intended direction. This exemplarymethod of the present invention detects whether the torque load on theblower motor 16 appears to be appropriate for the speed of the blower.For example, if a high blower speed and low torque is seen, the methoddeduces that the blower is turning in the wrong direction. The motorcontroller 18 therefore stops the motor 16 and electronically reversesits direction. The motor controller 18 then starts the motor 16 in theother direction and confirms the torque is appropriate for a givenspeed. When the higher torque is confirmed, the motor controller 18re-programs its memory to note the correct rotation for the nextstart-up. Similarly, other parameters such as motor speed could be usedto determine the correct rotation direction by comparing the speed ofrotation in either direction for a given torque. When the directionexhibiting the lower speed at the same torque is confirmed, the motorcontroller 18 re-programs its memory to note this direction as thecorrect rotation for the next start-up.

FIG. 12 shows another exemplary method 1200 for determining properrotation direction of a reversible motor in an HVAC system. Theparticular order of the elements in FIG. 12 and described herein can bealtered without departing from the scope of the invention. For example,some of the elements may be reversed, combined, or even removedentirely. In element 1202, a motor controller such as motor controller18 starts a motor, such as motor 16, to rotate the fan in a firstdirection. Since many HVAC systems are configured for CCW fan rotation,the motor controller may initially start the motor in the CCW direction,but it may be that the system requires CW direction. In element 1204,the motor controller or other mechanism monitors a torque load on themotor while the fan is rotated in the first direction. Other operatingparameters or characteristics other than torque load (such as power,airflow, or speed) may also be monitored. In element 1206, the motorcontroller determines if the monitored torque load or other parameter orcharacteristic is within an acceptable range. For example, if the motoris rated at 0.5 hp with a maximum rated torque of 30 inch-lbs., themotor controller or other mechanism may determine if the monitoredtorque is greater than about 20%, or about 6 inch-lbs. If it is, themethod stops at element 1208 and the motor controller thereafter alwaysrotates the motor in the first direction. However, if element 1206determines that the torque load is not within an acceptable range,element 1210 directs the motor controller to rotate the motor and fan ina second direction, in this example the CW direction. In element 1212,the motor controller or other mechanism monitors the torque load on themotor while the fan is rotated in the second direction. As would beunderstood by one skilled in the art, the parameter monitored in thesecond direction (i.e., the second parameter), may be the same parameteras was monitored in the first direction (i.e., the first parameter) or adifferent parameter, without departing from the scope of the embodimentsof the invention. In element 1214, the motor controller determines ifthe second monitored torque load is within the acceptable range. If itis, element 1216 changes a memory setting of the motor controller toindicate that the second direction is the proper rotation direction.Thereafter, the motor controller always rotates the motor in the seconddirection. If the motor torque load was not within an acceptable rangein either elements 1206 or 1214, element 1218 may provide an errormessage or may revert to element 1202 to start the method over.

FIG. 13 shows another exemplary method for determining proper rotationdirection of a reversible motor in an HVAC system. Method 1300 issimilar to method 1200 except that method 1300 takes into account both amonitored motor torque load (or other operating parameter orcharacteristic) and a fan speed. The particular order of the elements inFIG. 13 and described herein can be altered without departing from thescope of the invention. For example, some of the elements may bereversed, combined, or even removed entirely. Method 1300 starts withelement 1302 where the motor controller rotates the fan in a firstdirection. In element 1304, the motor controller or other mechanismmonitors a torque load on the motor while the fan is rotated in thefirst direction. In element 1306, the motor controller monitors arotation speed of the fan, either with a sensor or by controlling themotor to a desired speed, as in the described embodiment. Element 1308determines if the monitored torque load is appropriate for the monitoredrotation speed. Using the same 0.5 hp motor mentioned above as anexample, element 1302 may determine if the monitored torque isapproximately 6 inch-lbs, while the motor is rotating between about 500and about 800 RPMs, an acceptable range for this torque level. Othercomparisons may also be made, as long as the comparisons determinewhether the monitored torque load is appropriate for the monitoredblower speed. If the load is appropriate, method 1300 stops at element1308 and the motor controller thereafter always rotates the motor in thefirst direction. If the load is not appropriate, element 1312 operatesthe motor to rotate the fan in a second direction. Element 1314re-monitors the torque load on the motor while the fan is rotated in thesecond direction, and element 1316 monitors a rotation speed of the fanwhile the fan is rotated in the second direction. Element 1318determines if the second monitored torque load is appropriate for themonitored rotation speed for the second direction. If it is, element1320 changes a memory setting of the motor controller to indicate thatthe second direction is the proper rotation direction. If the motortorque load was not within an acceptable range in either elements 1306or 1314, element 1318 may provide an error message or may revert back toelement 1302 to start the method over.

Another embodiment of the invention provides methods to adjust thetorque settings of an HVAC blower motor. HVAC OEMs often desire blowermotors specifically designed to work with their HVAC equipment. Forexample, a blower motor manufacturer's typical 0.5 hp blower motor mayhave a maximum rated torque capability of 30 inch-lbs., but one OEM maydesire that the motor have a maximum rated torque capability of 27inch-lbs. (or 90%) and another OEM may desire a maximum rated torquecapability of 24 inch-lbs. (or 80%). With PSC motors, motormanufacturers can accommodate such requests by changing the motorwinding taps on their motors to achieve the desired torque ratings.Unfortunately, changing the motor taps to accommodate every OEM's exactspecifications is time-consuming and costly and requires that manyslightly modified motors be manufactured and stocked.

The present invention makes it easier to customize HVAC motors forparticular OEMs' needs by providing a method of adjusting the torquevalues of a blower motor without changing the motor's taps or otherwisealtering the motor's physical design. The methods are used with variablespeed motors such as those described above in connection with the otherembodiments of the present invention, but may be used with anyconventional motors.

An obstacle to adjusting the torque settings of an HVAC blower motor isthat most such motors have no accessible computer inputs or othercontrol inputs after they are manufactured. Instead, as disclosed above,known HVAC blower motors only have 2-5 exposed hot power inputs (e.g.,IN1-IN5), 1 or more neutral inputs (e.g. CW neutral and CCW neutral),and a ground input. Thus, the present invention's methods to adjust amotor's torque settings must be accomplished with these exposed inputs.

FIG. 14 illustrates a torque adjustment mechanism 60 constructed inaccordance with an embodiment of the invention that may be used by anHVAC OEM or anyone else to adjust the torque settings of a motor such asthe blower motor assembly 10 shown in FIG. 2 or the blower motorassembly 100 shown in FIG. 6. As illustrated, the torque adjustmentmechanism 60 only connects to the exposed power inputs of the blowermotor assembly.

The torque adjustment mechanism 60 may include a user interface, such asa selector switch 62, to select a torque adjustment for a particularHVAC system. Assume, for example, an OEM has XYZ and ABC models of HVACequipment. The XYZ model may be optimized with a blower motor having amaximum torque capability of 26.1 inch-lbs., and the ABC model may beoptimized with a blower model having a maximum torque capability of 28.5inch-lbs. The selector switch 62 of torque adjustment mechanism 60 maytherefore include an XYZ setting and an ABC setting. As would be readilyunderstood by one skilled in the art, the user interface may provide forselection between more than two settings or for the introduction ofuser-defined settings, as described below.

To adjust a motor's multiple torque settings, the torque adjustmentmechanism 60 is first attached to a motor's power input connections. Asused herein, the term multiple torque settings means two or more torquesettings, such as the five torque settings described below. For example,the torque adjustment mechanism may be attached to a 0.5 hp blower motorhaving a maximum torque capability of 30 inch-lbs. The motor may have 5power inputs with the following torque settings:

Standard Motor

IN1—100% 30 inch-lbs.

IN2—90% 27 inch-lbs.

IN3—80% 24 inch-lbs.

IN4—70% 21 inch-lbs.

IN5—30% 9 inch-lbs.

When this motor is attached to the torque adjustment mechanism and theselector is moved to the XYZ setting described above, the torqueadjustment mechanism adjusts the torque settings of the motor asfollows:

XYZ Motor

IN1—100% 26.1 inch-lbs.

IN2—90% 23.5 inch-lbs.

IN3—80% 20.9 inch-lbs.

IN4—70% 18.3 inch-lbs.

IN5—30% 7.8 inch-lbs.

Similarly, if the ABC setting is selected, the torque adjustmentmechanism adjusts the torque settings of the motor as follows:

ABC Motor

IN1—100% 28.5 inch-lbs.

IN2—90% 25.7 inch-lbs.

IN3—80% 22.8 inch-lbs.

IN4—70% 20.0 inch-lbs.

IN5—30% 8.6 inch-lbs.

FIG. 15 illustrates the circuitry of an embodiment of the torque adjustmechanism 60 in more detail. The circuitry may include a regulated DCpower supply 64 with a selector switch 65 and an isolated currentwaveform generator 66. The circuitry instructs the motor controller 18of the blower motor assembly 10 or 100 to change its torque settings byan adjustment factor indicated by the DC volts output by the DC powersupply 64. The selector switch 65 may have several positions (such asthe XYZ and ABC positions described above) or may permit the selectionof any DC output value within a range such as 60-100 volts(corresponding to 60% to 100% of the maximum rated torque of the motor).The output of the DC power supply 64 is connected to one of the powerinputs 38 of the power input connector 24 and the diode bridge rectifier12 of the blower motor assembly and charges the motor's DC bus to theselected voltage level (e.g. 60-100 volts). The isolated currentwaveform generator 66 is connected to two of the power inputs 44, 46 ofthe power input and includes an isolated 6-8 volt transformer T thatcharges a capacitor C with a DC load L. This generates an input currenton the power inputs 44, 46 identical to that of the blower motor duringits normal operation. This input current is routed into one of theinputs 44 and out of the other 46 while the DC power is applied to theDC bus to modify the torque settings of the motor in accordance with theoutput of the DC power supply. For example, if the selector switch 65 onthe DC power supply 64 is set to output 60 volts, all of the torquesettings of the motor are proportionally scaled down to 60% of theiroriginal values.

The motor controller 18 is programmed to recognize this otherwiseunusual circumstance of having current applied to it even though theapplied voltage is too low for the motor controller 18 to run the motorand draw any significant current. When the motor controller recognizesthis, it changes its torque settings in accordance with the inputvoltage.

A feedback mechanism may also be provided to indicate that the torquesettings of the motor have been changed. For example, the motor couldrun at no load to a specific RPM to indicate the new torque adjustmentfactor. An RPM of 600 could correspond to a 60% adjustment factor and anRPM of 1,000 could correspond to a 100% adjustment factor.

Instead of adjusting the torque as described above, the motor controller18 could store a plurality of different torque or speed tables andselect one of the torque/speed tables based on an input provided by thetorque adjustment mechanism. For example, when the torque adjustmentmechanism is attached to the blower motor assembly and set to output 60volts, the motor controller may select torque/speed table #1 from itsmemory, when the torque adjustment mechanism is set to output 61 volts,the motor controller may select table #2, etc.

Although the invention has been described with reference to theembodiments illustrated in the attached drawing figures, it is notedthat equivalents may be employed and substitutions made herein withoutdeparting from the scope of the invention as recited in the claims. Forexample, while the invention has been described in connection with 115VAC distribution systems, it is not limited to 115 VAC distributionsystems. One skilled in the art will recognize that, with obviousmodifications of implementation details, the invention may be adapted toother power distribution systems and voltages in use in the UnitedStates and elsewhere, including, but not limited to, 230 VACdistribution systems. Further, although many aspects of the presentinvention are particularly applicable to HVAC blower motors, they mayalso be used with electric motors designed for other applications.Moreover, all of the above-described embodiments of the invention areindependent of motor technology, and induction, brushless permanentmagnet, switched reluctance, brushed DC, and other types of motors maybe used. The invention is also compatible with a variety of convertertopologies, both for AC to DC and AC to AC conversion, including phasecontrol using a thyristor full converter or semiconverter. Relatedtechnologies are also disclosed in U.S. Pat. No. 5,818,194, which ishereby incorporated by reference in its entirety.

1. A method of adjusting torque values of a motor having multiple torquesettings and a maximum rated torque value, the method comprising:selecting an adjustment factor to obtain an adjusted maximum torquevalue that is less than the maximum rated torque value; adjusting allthe torque settings of the motor with the adjustment factor to obtainproportionally reduced torque settings; and operating the motor at theproportionally reduced torque settings.
 2. The method as set forth inclaim 1, wherein the adjustment factor is a percentage between 60% and99%.
 3. The method as set forth in claim 2, wherein the adjustmentfactor is between 80% and 95%.
 4. The method as set forth in claim 1,wherein the adjustment factor is selected based on characteristics of anHVAC enclosure in which the motor is to be mounted.
 5. The method as setforth in claim 1, wherein the proportionally reduced torque settings areobtained by multiplying the torque settings by the adjustment factor. 6.The method as set forth in claim 1, wherein the motor is a variablespeed motor.
 7. The method as set forth in claim 6, wherein the variablespeed motor is a brushless permanent magnet motor.
 8. A method ofadjusting torque values of an HVAC motor having multiple torque settingsand a maximum rated torque value, the method comprising: selecting anadjustment factor to obtain an adjusted maximum torque value that isless than the maximum rated torque value; selecting a torque tableassociated with the adjustment factor, the torque table includingalternate torque settings; and operating the motor at the alternatetorque settings.
 9. The method as set forth in claim 8, wherein theadjustment factor is a percentage between 60% and 99%.
 10. The method asset forth in claim 9, wherein the adjustment factor is between 80% and95%.
 11. The method as set forth in claim 8, wherein the adjustmentfactor is selected based on characteristics of an HVAC enclosure inwhich the motor is to be mounted.
 12. The method as set forth in claim8, wherein the table is selected from a plurality of different torquetables.
 13. The method as set forth in claim 8, wherein the HVAC motoris a variable speed motor.
 14. The method as set forth in claim 13,wherein the variable speed motor is a brushless permanent magnet motor.